Wiring Light to Arduino

I am currently trying to integrate a pair of NHL light pens into my project. I have taken apart the top portion that I want to use that contains the goal light/beacon and sound. Attached is a picture. I am not exactly sure how to hook it up to the Arduino and I think I need an experts opinion as I don’t want to fry my board. Here is how the thing works originally:

Batteries (LR44) are loaded between the positive(red wire with silver end) and negative (L shaped piece with black tape and silver end) leads.
When the button is pressed (connected to the 2 yellow wires) this completes the circuit which lights up the light and plays a sound byte.

Here is how I think I need to wire it up to the Arduino:

1.) Remove the button and Solder the two yellow wires together
2.) Wire red wire (+) into a PWR pin and tag pin as an output
3.) Clip the long L shaped piece with the black tape and replace with a wire. Wire this into ground on the arduino
4.) Code to power the thing on will be digitalWrite(pin, HIGH) or analogWrite(pin, HIGH).

I think I may be missing a resistor somewhere? I think I need to put a resistor attached to the red wire and then attach it to the PWR pin? Basically I am removing the button and using the Arduino to power the Light when I command it to via the code.

Thanks,
Scott

skuznarsky write (in part):

1.) Remove the button and Solder the two yellow wires together 2.) Wire red wire (+) into a PWR pin and tag pin as an output 3.) Clip the long L shaped piece with the black tape and replace with a wire. Wire this into ground on the arduino 4.) Code to power the thing on will be digitalWrite(pin, HIGH) or analogWrite(pin, HIGH).

(1) GOOD! You could even skip the yellow wires and just connect between the two pads on the board. (2) I don't understand what you mean by PWR pin. (3) GOOD! (4) NO!

You show two LR44 batteries. LR44 is 1.5 volts (nominal), so two batteries is 3.0 volts (nominal). Most Arduinos will output 0 and 5 volts. Nothing has been said about how much current the light pen uses or whether the circuit can handle 5 volts. You may need a source of 3 (3.3?) volts and a relay or transistor to control the light pen and to be operated by the Arduino.

You show two LR44 batteries. LR44 is 1.5 volts (nominal), so two batteries is 3.0 volts (nominal). Most Arduinos will output 0 and 5 volts. Nothing has been said about how much current the light pen uses or whether the circuit can handle 5 volts. You may need a source of 3 (3.3?) volts and a relay or transistor to control the light pen and to be operated by the Arduino.

Do you have a multimeter capable of measuring mA ?

Obviously the light pen must have a resistor hidden inside somewhere but as has already been pointed out you need to drop 2V so if you know the current as is before modification , using the shown LR44 batteries, then you can use that same current for your resistor calculation:

Let current = 20 mA

R = 2V/0.02 = 100 ohms

(1) GOOD! You could even skip the yellow wires and just connect between the two pads on the board. (2) I don't understand what you mean by PWR pin. (3) GOOD! (4) NO!

Sorry I meant a pin with PWM capability.

[/Do you have a multimeter capable of measuring mA ?quote]

I do have a multimeter and will have to check the mA.

So I have step 1 and step 3 right :). I am a little confused on how to power the thing. I understand that I will need a resistor to drop the voltage. After that will I be able to plug it into a Pin as an output? Please explain why NO! on step 4.

Thanks, Scott

How do I measure the mA running through this thing (IE where do I stick the black end and red end)? I have a multimeter but I never have had to use it.

Thanks, Scott

Has to be in-line, so in series. I.e., break the circuit and run it through the meter.

After hooking the light pen to a power supply I was able to find the current draw through the light is 6-7 mA. Using this I calculated the resistance needed to drop 2V is 333 ohms (2/.006). Now that I have that figured out my plan is to wire it as follows.

1.) get rid of button and solder the pads together (yellow wires on light's board) 2.) connect negative to ground on arduino 3.) connect + (red) to a 333 ohm resistor, connect resistor to wire and then to a pin on arduino 4.) code the pin to high when I want to light the lamp

I was told by an EE here that I really don't need to worry about using a transistor because of the low amperage/volts involved. Should I have any concerns with wiring as I mentioned above versus using a transistor?

Thanks, Scott